Understand Smallest Number From DI String Problem

Problem Name: Smallest Number From DI String

Problem Description:

Construct Smallest Number From DI String

Problem Statement

You are given a string pattern consisting of the characters:

'I' (Increasing): The next digit must be greater than the current one.
'D' (Decreasing): The next digit must be smaller than the current one.

Your task is to generate the smallest lexicographical number using digits 1-9 (without repetition) that follows this pattern.

Example 1

Input:
pattern = "IDID"

Output:
13254

Explanation:

1 < 3 (I)
3 > 2 (D)
2 < 5 (I)
5 > 4 (D)

Other possible numbers are "14253" and "15234", but "13254" is the smallest.

Example 2

Input:
pattern = "DDD"

Output:
4321

Explanation:

4 > 3 (D)
3 > 2 (D)
2 > 1 (D)

Other possible numbers like "9876" or "7654" are larger.

Constraints

1 <= pattern.length <= 8
pattern consists only of 'I' and 'D'.

Category:
Leetcode Problem of the Day
Stacks & Queues

Programming Language:
Java

Reference Link:

https://leetcode.com/problems/construct-smallest-number-from-di-string/description

Online IDE

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Java

Output:

Loading component...

Tracking code (View only. In case you want to track the code, click this button):

Main Function:

Main Function is not defined.

Helper Function:

INPUT: pattern = "IDID"

OUTPUT: 13254

public static String smallestNumber(String pattern) {

StringBuilder result = new StringBuilder();

Stack<Integer> stack = new Stack<>();

for (int i = 0; i <= pattern.length(); i++) {

stack.push(i + 1);

if (i == pattern.length() || pattern.charAt(i) == 'I') {

while (!stack.isEmpty()) {

result.append(stack.pop());

}//Loop End

}//If End